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SubjectRe: [PATCH] specific do_timer_cpu value for nohz off mode
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On Sun, 2012-01-15 at 14:46 +0100, Mike Galbraith wrote:
> On Tue, 2011-11-08 at 13:11 -0600, Dimitri Sivanich wrote:
> > Resending this.
> >
> >
> > Allow manual override of the tick_do_timer_cpu.
>
> Bigger button below.
>
> > While not necessarily harmful, doing jiffies updates on an application cpu
> > does cause some extra overhead that HPC benchmarking people notice. They
> > prefer to have OS activity isolated to certain cpus. They like reproducibility
> > of results, and having jiffies updates bouncing around introduces variability.
>
>
> > +#ifdef CONFIG_NO_HZ
> > + /* nohz mode not supported */
> > + if (tick_nohz_enabled)
> > + return -EINVAL;
> > +#endif
>
> Uhuh, we have something in common, your HPC folks don't like NO_HZ
> because it makes loads of jitter, my RT jitter test proggy hates it to
> pieces for the same reason. I can't just config it out like you though.
>
> Aside: how come your HPC folks aren't griping about (SGI monster) boxen
> ticking all at the same time? That makes my 64 core box jitter plenty.

P.S.

Using SGI and RT in the same message reminded me. I have the below in
my 3.0-rt tree, and 32 core UV100 box works fine. Wish I had a UV2 to
try out, the old (allegedly single digit s/n) UV1 is kinda slow.
Anyway, this patch is against mainline + preempt_rt FWIW.

rt,UV: rt conversion

Signed-off-by: Mike Galbraith <efault@gmx.de>

---
arch/x86/include/asm/uv/uv_bau.h | 12 ++++++------
arch/x86/kernel/apic/x2apic_uv_x.c | 6 +++---
arch/x86/platform/uv/tlb_uv.c | 18 +++++++++---------
arch/x86/platform/uv/uv_time.c | 21 +++++++++++++--------
4 files changed, 31 insertions(+), 26 deletions(-)
--- a/arch/x86/include/asm/uv/uv_bau.h
+++ b/arch/x86/include/asm/uv/uv_bau.h
@@ -518,8 +518,8 @@ struct bau_control {
unsigned short uvhub_quiesce;
short socket_acknowledge_count[DEST_Q_SIZE];
cycles_t send_message;
- spinlock_t uvhub_lock;
- spinlock_t queue_lock;
+ raw_spinlock_t uvhub_lock;
+ raw_spinlock_t queue_lock;
/* tunables */
int max_concurr;
int max_concurr_const;
@@ -670,15 +670,15 @@ static inline int atom_asr(short i, stru
* to be lowered below the current 'v'. atomic_add_unless can only stop
* on equal.
*/
-static inline int atomic_inc_unless_ge(spinlock_t *lock, atomic_t *v, int u)
+static inline int atomic_inc_unless_ge(raw_spinlock_t *lock, atomic_t *v, int u)
{
- spin_lock(lock);
+ raw_spin_lock(lock);
if (atomic_read(v) >= u) {
- spin_unlock(lock);
+ raw_spin_unlock(lock);
return 0;
}
atomic_inc(v);
- spin_unlock(lock);
+ raw_spin_unlock(lock);
return 1;
}

--- a/arch/x86/kernel/apic/x2apic_uv_x.c
+++ b/arch/x86/kernel/apic/x2apic_uv_x.c
@@ -56,7 +56,7 @@ int uv_min_hub_revision_id;
EXPORT_SYMBOL_GPL(uv_min_hub_revision_id);
unsigned int uv_apicid_hibits;
EXPORT_SYMBOL_GPL(uv_apicid_hibits);
-static DEFINE_SPINLOCK(uv_nmi_lock);
+static DEFINE_RAW_SPINLOCK(uv_nmi_lock);

static struct apic apic_x2apic_uv_x;

@@ -707,10 +707,10 @@ int uv_handle_nmi(unsigned int reason, s
* Use a lock so only one cpu prints at a time.
* This prevents intermixed output.
*/
- spin_lock(&uv_nmi_lock);
+ raw_spin_lock(&uv_nmi_lock);
pr_info("UV NMI stack dump cpu %u:\n", smp_processor_id());
dump_stack();
- spin_unlock(&uv_nmi_lock);
+ raw_spin_unlock(&uv_nmi_lock);

return NMI_HANDLED;
}
--- a/arch/x86/platform/uv/tlb_uv.c
+++ b/arch/x86/platform/uv/tlb_uv.c
@@ -39,7 +39,7 @@ static int timeout_base_ns[] = {
static int timeout_us;
static int nobau;
static int baudisabled;
-static spinlock_t disable_lock;
+static raw_spinlock_t disable_lock;
static cycles_t congested_cycles;

/* tunables: */
@@ -608,9 +608,9 @@ static void destination_plugged(struct b

quiesce_local_uvhub(hmaster);

- spin_lock(&hmaster->queue_lock);
+ raw_spin_lock(&hmaster->queue_lock);
reset_with_ipi(&bau_desc->distribution, bcp);
- spin_unlock(&hmaster->queue_lock);
+ raw_spin_unlock(&hmaster->queue_lock);

end_uvhub_quiesce(hmaster);

@@ -630,9 +630,9 @@ static void destination_timeout(struct b

quiesce_local_uvhub(hmaster);

- spin_lock(&hmaster->queue_lock);
+ raw_spin_lock(&hmaster->queue_lock);
reset_with_ipi(&bau_desc->distribution, bcp);
- spin_unlock(&hmaster->queue_lock);
+ raw_spin_unlock(&hmaster->queue_lock);

end_uvhub_quiesce(hmaster);

@@ -649,7 +649,7 @@ static void disable_for_congestion(struc
struct ptc_stats *stat)
{
/* let only one cpu do this disabling */
- spin_lock(&disable_lock);
+ raw_spin_lock(&disable_lock);

if (!baudisabled && bcp->period_requests &&
((bcp->period_time / bcp->period_requests) > congested_cycles)) {
@@ -668,7 +668,7 @@ static void disable_for_congestion(struc
}
}

- spin_unlock(&disable_lock);
+ raw_spin_unlock(&disable_lock);
}

static void count_max_concurr(int stat, struct bau_control *bcp,
@@ -717,7 +717,7 @@ static void record_send_stats(cycles_t t
*/
static void uv1_throttle(struct bau_control *hmaster, struct ptc_stats *stat)
{
- spinlock_t *lock = &hmaster->uvhub_lock;
+ raw_spinlock_t *lock = &hmaster->uvhub_lock;
atomic_t *v;

v = &hmaster->active_descriptor_count;
@@ -1835,7 +1835,7 @@ static int __init uv_bau_init(void)
}

nuvhubs = uv_num_possible_blades();
- spin_lock_init(&disable_lock);
+ raw_spin_lock_init(&disable_lock);
congested_cycles = usec_2_cycles(congested_respns_us);

uv_base_pnode = 0x7fffffff;
--- a/arch/x86/platform/uv/uv_time.c
+++ b/arch/x86/platform/uv/uv_time.c
@@ -58,7 +58,7 @@ static DEFINE_PER_CPU(struct clock_event

/* There is one of these allocated per node */
struct uv_rtc_timer_head {
- spinlock_t lock;
+ raw_spinlock_t lock;
/* next cpu waiting for timer, local node relative: */
int next_cpu;
/* number of cpus on this node: */
@@ -178,7 +178,7 @@ static __init int uv_rtc_allocate_timers
uv_rtc_deallocate_timers();
return -ENOMEM;
}
- spin_lock_init(&head->lock);
+ raw_spin_lock_init(&head->lock);
head->ncpus = uv_blade_nr_possible_cpus(bid);
head->next_cpu = -1;
blade_info[bid] = head;
@@ -232,7 +232,7 @@ static int uv_rtc_set_timer(int cpu, u64
unsigned long flags;
int next_cpu;

- spin_lock_irqsave(&head->lock, flags);
+ raw_spin_lock_irqsave(&head->lock, flags);

next_cpu = head->next_cpu;
*t = expires;
@@ -244,12 +244,12 @@ static int uv_rtc_set_timer(int cpu, u64
if (uv_setup_intr(cpu, expires)) {
*t = ULLONG_MAX;
uv_rtc_find_next_timer(head, pnode);
- spin_unlock_irqrestore(&head->lock, flags);
+ raw_spin_unlock_irqrestore(&head->lock, flags);
return -ETIME;
}
}

- spin_unlock_irqrestore(&head->lock, flags);
+ raw_spin_unlock_irqrestore(&head->lock, flags);
return 0;
}

@@ -268,7 +268,7 @@ static int uv_rtc_unset_timer(int cpu, i
unsigned long flags;
int rc = 0;

- spin_lock_irqsave(&head->lock, flags);
+ raw_spin_lock_irqsave(&head->lock, flags);

if ((head->next_cpu == bcpu && uv_read_rtc(NULL) >= *t) || force)
rc = 1;
@@ -280,7 +280,7 @@ static int uv_rtc_unset_timer(int cpu, i
uv_rtc_find_next_timer(head, pnode);
}

- spin_unlock_irqrestore(&head->lock, flags);
+ raw_spin_unlock_irqrestore(&head->lock, flags);

return rc;
}
@@ -300,13 +300,18 @@ static int uv_rtc_unset_timer(int cpu, i
static cycle_t uv_read_rtc(struct clocksource *cs)
{
unsigned long offset;
+ cycle_t cycles;

+ migrate_disable();
if (uv_get_min_hub_revision_id() == 1)
offset = 0;
else
offset = (uv_blade_processor_id() * L1_CACHE_BYTES) % PAGE_SIZE;

- return (cycle_t)uv_read_local_mmr(UVH_RTC | offset);
+ cycles = (cycle_t)uv_read_local_mmr(UVH_RTC | offset);
+ migrate_enable();
+
+ return cycles;
}

/*



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